The present invention relates to a steel product that can be used in abrasion resistant applications and to methods for manufacturing such an abrasion resistant steel product.
In general, the flow of materials across a steel surface has a tendency to abrade or erode the steel over time. Accordingly, the steel industry has developed specific products for these types of applications. Wear plates are one example. Wear plates are often found in conveyor systems and material handling chutes. Materials that often flow across wear plates causing the wear plates to degrade include coal, gravel, minerals, wheat, and corn. Because wear plates have a tendency to erode over time, they are often designed to be replaceable. Therefore, once a wear plate has abraded or eroded to a certain extent, it is often merely removed and replaced with a new one.
Because of the abrasive environment in which wear plates are used, industry has sought to manufacture steel with a relatively high degree of surface hardness and a relatively high degree of abrasion resistance. Unfortunately, this specialized steel, while exhibiting excellent wear characteristics, has some short comings. Often this product is brittle and cannot withstand mild bending that may be necessary for installation or use of the product. Due to the desire of end users to avoid premature breakage in service and perform mild bending of wear plates for some applications, some degree of formability is highly desirable. In addition, during the heat treatment of currently available abrasion resistant bar products, the bar product experiences varying degrees of distortion, which requires the product to be straightened. Currently available products do not have the ability to consistently withstand the mild bending required for straightening and subsequent breakage can result in significant losses in both time (extra time to straighten) and material. In many cases currently available abrasion resistant material cannot be straightened due to its relatively low ductility and is unacceptable to customers. This inability to straighten is such significant problem that wear resistant shapes have never been hot rolled and heat treated as a single piece. For this reason, wear resistant flats have often been manufactured by slitting large plates adding cost and inconvenience. The present invention provides a new abrasion resistant type steel and a process for preparing such abrasion resistant steel. The present invention or the first time provides mild formability for both the end application and manufacturing straightening process.
The present invention describes a hardened steel product comprising
(i) at least about 96 wt. % iron;
(ii) between about 0.24 wt. % and about 0.30 wt. % carbon;
wherein;
(iii) the steel product has a Brinell hardness according to ASTM A370 of greater than 360 Bhn; and
(iv) an elongation according to ASTM A370 of at least about 8 percent at a two inch gauge.
The hardened steel product can be, but need not be, prepared by the following process, comprising steps of:
(a) providing a steel product comprising at least about 96 wt. % iron and between about 0.20 wt. % and about 0.30 wt. % carbon;
(b) heating the steel product to at least its austentizing point;
(c) quenching the steel product to temperature below its martensite finish temperature; and
(d) tempering the steel product at a temperature of at least about 850xc2x0 F. to provide a hardened steel product having a surface hardness of greater than about 360 Bhn.
The present invention is the first demonstration of an abrasion resistant steel product that can withstand mild bending necessary for either straightening or for required installation manipulations. The product is manufactured by counterintuitive balance between a relatively high carbon level and a surprisingly high tempering temperature. This balance results in the hardened steel product""s unique characteristics. The present invention provides the opportunity to prepare abrasion resistant shapes in a single hot rolling and subsequent heat treating process. To date these shapes must be manufactured by welding numerous pieces together. Because of the cost of this welding step, many uses of abrasion resistant shapes have not been exploited. The present invention will allow for the hot rolling, tempering, and straightening of shapes for the first time. In addition, the surprising formability of the present invention will enable the use of abrasion resistant steel in many new applications. For many users of abrasion resistant steel products the formability is an essential requirement for the steel""s application.